1. Field of the Invention
The present invention relates to a capping device for an ink jet nozzle, and more particularly to such capping device capable of preventing defective printing caused by uneven wetting of the nozzle face at the suction recovery step of the nozzle.
2. Description of the Prior Art
As already known, an ink jet nozzle is utilized as the recording head for a recording apparatus in which liquid ink is emitted for recording on a printing sheet in response to electric signals. When such ink jet nozzle is subjected to a mechanical shock or a sudden temperature change, air enters the nozzle to destroy the normal meniscus, thus disabling the ink emission in response to electric signals. In order to resolve such non-emitting state, the nozzle is sucked from the front end thereof, thus restoring the normal meniscus. However, when the cap for the suction is lifted, ink may locally remain on the front end of the nozzle.
The above-mentioned phenomenon is more detailedly shown in FIGS. 1 to 3, wherein a recording head 1 positioned in an unrepresented carriage and integral with a sub-tank is provided with multiple nozzles 2. The outer diameter of each nozzle is in the order of 0.4 mm. In case of defective printing such as the lack of ink emission, a cap 3 moves toward the nozzles 2 to tightly cover said nozzles through an elastic member 4. A suction pump 6 is activated in this state to generate a negative pressure in a space 7 through a pipe 5, whereby the ink is extracted from the nozzles into the space 7. An air layer or other substance in the nozzle hindering the ink emission is ejected from the nozzle, thus enabling the ink emission. However, when the cap is lifted in the direction of arrow shown in FIG. 2, the extracted ink 8 is pulled in both directions by the nozzles and by the cap due to surface tension, and a part of said ink remains around the nozzles even if it is made water-repellent, whereby an ink pool 9 is formed around the nozzles. The ink emission is quite often hindered if such an ink pool exists. Also such an ink pool is apt to appear in the case of a multiple-nozzle recording head, since the space 7 of the elastic member 4 inevitably has an oval cross section with a reduced ink holding ability.